Fatigue resistance of denture teeth

AIMS: There is no standard test to determine the fatigue resistance of denture teeth. With the increasing number of patients with implant-retained dentures the mechanical strength of the denture teeth requires more attention and valid laboratory test set-ups. The purpose of the present study was to determine the fatigue resistance of various denture teeth using a dynamic load testing machine. METHODS: Four denture teeth were used: Bonartic II (Candulor), Physiodens (Vita), SR Phonares II (Ivoclar Vivadent) and Trubyte (Dentsply). For dynamic load testing, first upper molars with a similar shape and cusp inclination were selected. The molar teeth were embedded in cylindrical steel molds with denture base material (ProBase, Ivoclar Vivadent). Dynamic fatigue loading was carried out on the mesio-buccal cusp at a 45° angle using dynamic testing machines and 2,000,000 cycles at 2Hz in water (37°C). Three specimens per group and load were submitted to decreasing load levels (at least 4) until all the three specimens no longer showed any failures. All the specimens were evaluated under a stereo microscope (20× magnification). The number of cycles reached before observing a failure, and its dependence on the load and on the material, has been modeled using a parametric survival regression model with a lognormal distribution. This allowed to estimate the fatigue resistance for a given material as the maximal load for which one would observe less than 1% failure after 2,000,000 cycles. RESULTS: The failure pattern was similar for all denture teeth, showing a large chipping of the loaded mesio-buccal cusp. In our regression model, there were statistically significant differences among the different materials, with SR Phonares II and Bonartic II showing a higher resistance than Physiodens and Trubyte, the fatigue resistance being estimated at around 110N for the former two, and at about 60N for the latter two materials. CONCLUSION: The fatigue resistance may be a useful parameter to assess and to compare the clinical risk of chipping and fracture of denture tooth materials.

Rigid Rod Polymer Fillers in Acrylic Denture and Dental Adhesive Resin Systems

Polymeric materials have been used in dental applications for decades. Adhesion of polymeric materials to each other and to the tooth substrate is essential to their successful use. The aim of this series of studies was two-folded. First, to improve adhesion of poly(paraphenylene) based rigid rod polymer (RRP) to other dental polymers, and secondly, to evaluate the usability of a new dentin primer system based on RRP fillers. Poly(paraphenylene) based RRP would be a tempting material for dental applications because of its good mechanical properties. To be used in dental applications, reliable adhesion between RRP and other dental polymers is required. In this series of studies, the adhesion of RRP to denture base polymer and the mechanical properties of RRP-denture base polymer-material combination were evaluated. Also adhesion of BisGMA-TEGDMA-resin to RRP was determined. Different surface treatments were tested to improve the adhesion of BisGMA-TEGDMA-resin to RRP. Results were based on three-point bending testing, Vickers surface hardness test and scanning electron microscope analysis (SEM), which showed that no reliable adhesion between RRP and denture base polymer was formed. Addition of RRP filler to denture base polymer increased surface hardness and flexural modulus but flexural strength decreased. Results from the shear bond strength test and SEM revealed that adhesion between resin and RRP was possible to improve by surface treatment with dichloromethane (DCM) based primer and a new kind of adhesive surface can be designed. The current dentin bonding agents have good immediate bond strength, but in long term the bond strength may decrease due to the detrimental effect of water and perhaps by matrix metalloproteinases. This leads to problems in longevity of restorations. Current bonding agents use organic monomers. In this series of studies, RRP filled dentin primer was tested in order to decrease the water sorption of the monomer system of the primers. The properties of new dentin primer system were evaluated in vitro by comparing it to commercial etch and rinse adhesive system. The results from the contact angle measurements and SEM showed that experimental primer with RRP reinforcement provided similar resin infiltration to dentin collagen and formed the resin-dentin interface as the control primer. Microtensile bond strength test and SEM revealed that in short term water storing, RRP increased bond strength and primer with BMEP-monomer (bis[2-(methacryloyloxy)-ethyl]phosphate) and high solvent concentration provided comparable bonding properties to the commercial control primers. In long term water storing, the high solvent-monomer concentration of the experimental primers decreased bond strength. However, in low solvent-monomer concentration groups, the long-term water storing did not decrease the bond strength despite the existence of hydrophilic monomers which were used in the system. These studies demonstrated that new dentin primer system reached the mechanical properties of current traditional etch and rinse adhesive system in short time water storing. Improved properties can be achieved by further modifications of the monomer system. Studies of the adhesion of RRP to other polymers suggest that adhesion between RRP and other dental polymers is possible to obtain by certain surface treatments.

Resolución N° 10 ¿Puede la Cámara de Comercio ordenar la suspensión provisional de actos administrativos de registro? ¿Qué documentos son objeto de estudio por parte de la CCB?

Servicios registrales

Article of agreement between Alexander Cook, contractor of Humberstone and the Provisional Municipal Council of the county of Welland

Article of agreement between Alexander Cook, contractor of Humberstone and the Provisional Municipal Council of the county of Welland to construct and build the main drain through the marsh lands tract commencing in lot no. 27 in the 4th concession in the township of Humberstone in a southerly direction (6 pages, handwritten). This is signed by John Frazer, Provisional Warden, Dexter Deverardo and Alexander Cook. (2 copies), Dec. 30, 1854.

Extract from the minutes of a session of the Provisional Municipal Council of the County of Welland

Extract from the minutes of a session of the Provisional Municipal Council of the County of Welland held on Nov. 3rd, 1855. It was decided that the petition of Andrew Drew and others be laid over until the engineer could make a survey of the premises and report to the council. This was signed by Dexter Deverardo, 1855

Convenio militar para la suspensión provisional de las hostilidades

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Manifiesto de la suprema junta provisional gubernativa, con el testimonio de su disolución.

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Mensage del Exmo. Sr. Presidente provisional de la República, D. Manuel de la Peña y Peña : leído en la apertura de las sesiones del Congreso de 1848.

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Diario de las sesiones de la Soberana Junta Provisional gubernativa del imperio mexicano, instalada según previenen el plan de Iguala y tratados de Villa de Córdova.

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Colección de los documentos mas importantes relativos a la instalación y reconocimiento del gobierno provisional del escmo. sr. Presidente de la suprema corte de Justicia

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Estatuto Provisional del Imperio Mexicano

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[Discurso dirigido al Honorable Congreso Constituyente del Estado libre de Querétaro, al tiempo de su instalación, verificada el día 17 de Febrero de 1824 por el Gefe Superior Político y Militar como Presidente de la Escma. Diputación Provisional, que cesó en aquel dia sus penciones

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Manifiesto del gobierno provisional a la nación : acerca de los negocios de Yucatán

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Constituciones de la imperial orden de Guadalupe : instituída por la junta provisional gubernativa del imperio, á propuesta del serenísimo señor generalísimo almirante Don Agustín de Iturbide, en 18 de Febrero de 1822

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Coleccion de ordenes y decretos de la Soberana Junta provisional gubernativa, y soberanos Congresos generales de la nacion mexicana.

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